A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of this patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
A computer program listing appendix is submitted herewith on a single compact disc. The computer program listing is incorporated-by-reference herein its entirety. The compact disc is a CD-R disc labeled xe2x80x9c09/398,547apxxe2x80x9d and contains a single computer program listing that was saved to CD-R on Aug. 6, 2002 and is 3.5 MB.
The present invention relates to density detection using discrete photon counting, and more particularly to using discrete photon counting to generate an image indicative of the densities in a target object. Even more particularly, the invention relates to using discrete photon counting in ultra high-speed real time detection, and distortion-free image processing for a fast-moving target, under acceleration.
There are many-instances in the security or customs field when it is necessary to examine or inspect, in a non-destructive way, the contents of a target object, such as a closed package, box, suitcase, cargo container, automobile semi-trailer, tanker truck, railroad car, e.g., box car or tanker car, or the like. For example, customs departments are routinely charged with the responsibility of inspecting vehicles coming into a country to make sure such packages do not contain drugs or other contraband, or leaving the country with stolen automobiles, drug money, and other illicit contraband. Similarly, drug smugglers frequently carry out their criminal acts by hiding illegal drugs in vehicles such tanker trucks, and then sending the trucks through a border checkpoint. When security personnel encounter suspicious vehicles or other containers being transported over international boundaries, they must perform a careful inspection of such vehicles to ascertain their contents. Similarly, when suspicious trucks or cars enter compounds overseas having U.S. troops or containing embassy offices, they must be inspected for hidden vehicle bombs, poisonous gases, etc.
When suspicious vehicles are discovered, they generally must be examined or inspected on location in what is referred to as a xe2x80x9csecondary inspection area.xe2x80x9d If secondary inspection reveals the presence of contraband (e.g., drugs), then the vehicle may be impounded, the driver arrested, and the contraband disposed of. If, on the other hand, the examination reveals the absence of contraband, then the vehicle may be allowed to proceed in a normal manner.
The process used to examine or inspect a suspicious vehicle should be quick, simple, as unintrusive as possible and fast enough so as to not impede the xe2x80x9cflow of commercexe2x80x9d. Unfortunately, most common conventional inspection mechanisms require either visual inspection by others and/or scent inspection by dogs.
These conventional inspection methods require that the vehicle stop and wait for the inspection to be completed, which can take a half hour or more. This is both inconvenient and time consuming for both customs officials and the vehicle drivers and occupants. Furthermore, such inspection may put officers at personal risk if a vehicle has been booby-trapped or if the vehicle""s driver or other occupants become nervous and decide to attack the customs officer inspecting their vehicle. What is needed, therefore, is a non-invasive technique for inspecting the contents of a suspicious vehicle without requiring that the vehicle be stopped and manually inspected.
One attempt to satisfy this need involves the use of high levels of radiation to determine the densities of the vehicle and/or the contents of such vehicle. Unfortunately, this approach in the prior art requires that the vehicle be stopped and evacuated prior to inspection, because such high levels of radiation can be physically harmful to the vehicle""s occupants if they remain in the vehicle during inspection.
Disadvantageously, prior art inspection systems using high levels of radiation not only require that the vehicle be stopped, and therefore delayed, but pose a risk to stowaways that may be aboard the vehicle, and unwilling to voluntarily evacuate when the vehicle is stopped for inspection. Therefore, what is needed is a non-invasive technique for inspecting the contents of a suspicious vehicle without requiring the use of high levels of radiation.
A further problem posed by manual inspection techniques arises when tanker trucks or railroad cars, after having been emptied, seek to cross a border in order to refill. Because some such tankers (e.g., liquified petroleum gas tankers that are of thick, double-walled steel construction) cannot be completely emptied without releasing the pressure in such tankers and venting noxious (and explosive) gasses into the atmosphere, the tankers typically are kept nominally under pressure. (The venting of noxious gasses would be hazardous and ecologically unacceptable.) Thus, the contents of such tankers typically go uninspected by customs agents in order to avoid the time-consuming (up to 3 days, with nitrogen purging) venting of such gases. Unfortunately, drug smugglers are well aware of this fact, and therefore utilize tanker trucks and railroad cars to import illegal drugs, knowing that they will not be inspected at the border. This venting condition provides just one of numerous additional examples of cases where invasive or intrusive inspection into vehicles, or other containers, is not feasible or desirable. Thus, this venting condition further emphasizes the need for a non-intrusive approach to vehicle inspection, especially by a high-energy gamma-ray radiographic system that easily penetrates the steel walled tanker.
Yet a further problem with prior vehicle inspection systems is that some, employing inspection sources, move a vehicle past a source and detector with heavy equipment subject to frequent breakdowns, and requiring very high capital costs for installation. Some inspect at a rate as low as 10-15 minutes per cargo vehicle, according to U.S. Customs Inspectors.
Additionally, some prior systems employing a high intensity standard X-ray radiation source require from xc2xd hour to 1 hour to warm up, depending upon the intervals between use. The X-ray source is expensive to buy and to install and requires an appreciable amount of power to operate, is sensitive to ambient humidity, and is expensive and time-consuming to repair.
Furthermore, these expensive X-ray sources also require a permanent shielding structure, which, along with the vehicle-moving mechanism, boosts the capital costs to nearly $10,000,000 for one such system, limiting the numbers which can be in use at borders.
Therefore, there is a widely known need in the industry of cargo-vehicle inspection systems for a mobile, vehicle inspection system capable of detecting contraband on the order of less than a pound (or better) in a large, fast-moving vehicle, with the use of relatively very low intensity radiation (on the order of Curie or better), in a manner which can be done swiftly so as not to hold up vehicle traffic at border inspection points, and affordably, even with a fast-moving, large, accelerating vehicle, accelerating at an unpredictable rate.
The present invention advantageously addresses the above and other needs.
The present invention advantageously addresses the needs above as well as other needs by providing a system and method employing discrete photon counting, and a relatively very low intensity radiation source, to perform ultra high-speed real-time density measurements in a fast-moving, target object and to generate a distortion-free, high resolution image of contents of such fast-moving (and accelerating), target object in response thereto.
In one embodiment, the invention is characterized as a system for detecting and graphically displaying contents of a fast-moving target object comprising: a radiation source, having a position such that at least a portion of radiation emitted from the radiation source passes through the fast-moving target object, the fast-moving target object having a variable velocity and acceleration while maintaining a substantially constant distance from the radiation source and being selected from the group consisting of: a vehicle, a cargo container, and a railroad car; a velocity measuring device configured to measure the variable velocity of the fast-moving target object; a detector array comprising a plurality of photon detectors, having a position such that at least some of the at least a portion of the radiation passing through the fast-moving target object is received thereby, the detector array having a variable count time according to the variable velocity and a grid unit size; a counter circuit coupled to the detector array for discretely counting a number of photons entering individual photon detectors of the detector array, the counter circuit measuring a count rate according to a contents within the fast-moving target object; a high baud rate interface coupled to the counter circuit for sending count information from the counter circuit at a rate fast enough to support real-time data transfer therethrough; and a processor coupled to the velocity measuring device and to the high baud-rate interface, receiving count information from the high baud-rate interface and generating distortion-free image data in real time as a function of the count information and the variable velocity.
In another embodiment a method of detecting and graphically displaying without distortion, in real time, a contents of a fast-moving target object comprises the steps of: directing photons from a radiation source toward the fast-moving target object having a variable velocity and acceleration while maintaining a substantially constant distance from the radiation source, and being selected from the group consisting of: a vehicle, a cargo container, and a railroad car; receiving at least a portion of the photons directed at the fast-moving target object at a detector array maintaining substantial equidistance from the radiation source; measuring the variable velocity and acceleration of the fast-moving target with a velocity measuring device coupled to a processor; discretely counting a number of the photons entering each of a plurality of detectors in the detector array with a counter circuit at a count rate according to the contents; sending count data on the number of photons from the counter circuit to the processor through a high baud-rate interface at a processing rate fast enough to support real-time data transfer from the counter circuit; receiving the count data at a graphical display device from the processor; and generating distortion-free image data in real time, as a function of the count data and the variable velocity of the contents of the fast-moving target object.
In a variation of the above method, a method of detecting a density, without distortion, within a fast-moving target object, includes performing the above steps for radiation passing through a first and second volume of the fast-moving target object, hitting a first and second radiation detector.
In a further embodiment, a method of vehicle inspection employs a mobile platform in a moving target mode, to detect and graphically display, in real time, without distortion, a contents of a fast-moving target object. The method comprises the steps of: positioning a mobile platform having a boom and a detector array tower thereon; wherein the boom has a radiation source, and wherein the detector array tower houses a detector array; deploying the boom to a distance and configuration relative to the mobile platform and the detector array tower sufficient to allow passage of a vehicle therethrough; accelerating, from a stationary position, the fast-moving target object between the detector array tower and the radiation source so as to maintain a substantially equal distance from the radiation source; directing photons from the radiation source toward the fast-moving target object upon acceleration of the fast-moving target object; receiving at least a portion of the photons directed at the fast-moving target object at the detector array; measuring the variable velocity and acceleration of the fast-moving target with a velocity measuring device coupled to a processor; discretely counting a number of the photons entering each of a plurality of detectors in the detector array with a counter circuit measuring a count rate according to the contents; sending count data on the number of photons from the counter to the processor through a high baud-rate interface in real-time data; receiving the count data at a graphical display device from the processor; and generating distortion-free image data in real time as a function of the count data and the variable velocity and acceleration of the contents.
In a variation of the above embodiment, a mobile platform can be used in a stationary target mode, by accelerating the mobile platform and performing analogous steps.
In yet a further embodiment, the invention can be characterized as a linear detector array system for use in a vehicle inspection system for detecting a contents of a fast-moving target object. The linear detector array comprises: a plurality of vertical rows of staggered detectors, each of the plurality of vertical rows being vertically staggered from, yet not overshadowing, each other vertical row, such that a pitch between any two closest adjacent staggered detectors is smaller than a diameter of the staggered detectors.
In yet a further embodiment, a method for processing staggered detection data for use in a vehicle inspection system, comprises the steps of: providing a plurality of vertical rows of staggered detectors, each of the plurality of vertical rows being vertically plurality of vertical rows of staggered detectors, each of the plurality of vertical rows being vertically staggered from, yet not overshadowing, each other vertical row, such that a pitch between any two closest adjacent staggered detectors is smaller than a diameter of the staggered detectors; including: providing a center vertical row of staggered detectors; providing one or more side vertical rows of staggered detectors; providing a processor comprising an image-generating program; receiving data at the processor from each of the one or more side vertical rows and from the center vertical row; determining an adjustment for a horizontal displacement k of the one or more side vertical rows using the adjustment to coincide data from the side vertical rows with data from the center vertical row. In this embodiment the three (or any n number of) rows of detectors are used rather than a single row of appreciably smaller detectors, so that a higher detector count rate can be achieved. This improves inspection speeds at a given source strength.